In general, washing machines, for example, drum washing machines, are apparatuses which include a tub for storing water (washing water or rinsing water), a drum rotatably installed inside the tub and accommodating laundry and a motor that generates a driving force for rotating the drum and in which, when the drum is rotated, the laundry inside the drum ascends or descends along inner walls of the drum so that the contaminated laundry can be washed.
A laundry port through which the laundry can be put into or taken out of the inside of the drum, is formed in the washing machine, and a door is disposed to open/close the laundry port. Thus, a user opens the door to take or put the laundry out of or into the drum.
When an operation of the washing machine starts to perform, the door is kept in a locked state. Thus, when the user wants to additionally put the laundry, the user needs to open the door. In order to open the door during the operation of the washing machine, it has to be waited until a washing cycle is finished, or supplied water has to be drained. In this way, it is not easy to additionally put the laundry during the operation of the washing machine.